The present invention relates to absorbent materials that, upon contacting liquids such as water or body fluids, swell and imbibe such liquids. More specifically, the present invention relates to improved structural stability in the dry and wet states of absorbent materials. The absorbent material of the present invention has particular applicability to absorbent articles such as diapers, adult incontinence pads, sanitary napkins, and the like.
Water-insoluble, water-swellable, hydrogel-forming absorbent polymers are capable of absorbing large quantities of liquids such as water, body fluids (e.g., urine, blood, menstrual fluid), industrial fluids and household fluids and are further capable of retaining such absorbed liquids under moderate pressures. These absorption characteristics of such polymer materials make them especially useful for incorporation into absorbent articles such as disposable diapers, adult incontinence pads and briefs, and catamenial products such as sanitary napkins, and the like.
The development of highly absorbent members used in such absorbent articles are the subject of substantial commercial interest. A highly desired characteristic for such absorbent articles is thinness. For example, thinner diapers are less bulky to wear, fit better under clothing, and are less noticeable. They are also more compact in the package, making the diapers easier for the consumer to carry and store. Compactness in packaging also results in reduced distribution costs for the manufacturer and distributor, including less shelf space required in the store per diaper unit.
The ability to provide thinner absorbent articles such as a diaper has been contingent on the ability to develop relatively thin absorbent cores or structures that can acquire and store large quantities of discharged body fluids, particularly urine. In this regard, the use of certain absorbent polymers often referred to as xe2x80x9chydrogelsxe2x80x9d xe2x80x9csuperabsorbentsxe2x80x9d or xe2x80x9chydrocolloidxe2x80x9d material, has been particularly important. See, for example, U.S. Pat. No. 3,699,103 (Harper et. al), issued Jun. 13, 1972, and U.S. Pat. No. 3,670,731 (Harmon), issued Jun. 20, 1972, that disclose the use of such absorbent polymers (hereafter xe2x80x9cwater-insoluble absorbent hydrogel-forming polymersxe2x80x9d) in absorbent articles.
Moreover, prior absorbent articles have generally comprised relatively low amounts (e.g., less than about 50% by weight) of absorbent gelling particles of the WAHPs. See, for example, U.S. Pat. No. 4,834,735 (Alemany et. al), issued May 30, 1989. It discloses that an absorbent structure or core contains preferably from about 9 to about 50% of WAHP in the fibrous matrix. Unfortunately several problems are encountered when one attempts to provide a thin absorbent core having more than 50% concentration of absorbent gelling particles by weight.
Conventional absorbent articles have the limitation that the absorbent gelling particles are not immobilized and are free to migrate(shift) during the manufacturing process and/or use(wearing). Migrations(shifting) of the absorbent gelling particles during manufacture can lead to absorbent material handling losses during manufacturing operations as well as nonhomogerous incorporation of the particles being used. A more significant problem, though, occurs when these absorbent gelling particles of WAHPs migrate during or after swelling. This inability to fix the particles at optimum locations leads to an insufficient urine storage capacity in one area and over-capacity in other areas due to the lack of stability.
One important factor is to minimize and/or eliminate the shifting of particles of WAHPs from the first applying location to another position and handling losses during manufacture.
One problem encountered is the shifting and/or leakage of swollen (e.g., with urine) particles of WAHP due to wear-related movement and pressure on the absorbent article. The inability to fix the particles at optimum location is another issue that results in insufficient urine storage capacity in one area and over-capacity in other areas. Subsequently the absorbent article will leak during use. The shifting of wet particles of WAHPs can cause core shifting and more incidence of gel leakage when in use, especially from an absorbent material containing high concentration of WAHPs.
Yet another important factor that has to be considered is the liquid permeability of WAHPs. It has been discovered that the permeability or flow conductivity of the gel layer formed by swelling in the presence of body fluids is extremely important when these absorbent polymers are used in absorbent cores or members at a high concentration in localized or throughout regions thereof. It should be noted that lack of liquid permeability or flow conductivity of absorbent polymers may directly impact on the ability of resultant gel layers to acquire and distribute body fluids.
Still another concern of WAHPs used in thinner absorbent article is the jelly and mushy feel when touching and handling the absorbent article after usage. When WAHP is dispersed in region or regions at a high concentration, the swollen gel formed by absorbing body fluids is a gel layer, in which the particulate is mobile and the gel layer collapses when subjected to forces such as pushing, squeezing, etc. when handling the absorbent article after usage. This is why absorbent articles having high concentration of WAHP give users or consumers xe2x80x9cwet/mushyxe2x80x9d feel when touching or handling them from outside.
Therefore, the present invention seeks to resolve the above problems by providing an absorbent material having improved structural stability in dry and wet status.
Briefly stated, the present invention relates to absorbent materials having improved structural stability in dry and wet states. These absorbent materials comprise (a) absorbent gelling particles comprising a water-insoluble absorbent hydrogel-forming polymer; (b) a polycationic polymer; (c) glue microfibers; and (d) a carrier layer; wherein the polycationic polymer is bonded to the absorbent gelling particles; and the glue microfibers act as an adhesive between the absorbent gelling particles and the carrier layer. Because the glue microfibers are tacky, the absorbent gelling particles comprising a WAHP fix to the desired location on the carrier layer and do not shift to the another area in dry state. In wet state, when the absorbent material contacts liquids such as body fluids, the absorbent gelling particles contained in the absorbent material fix to the location first applied due to bonding of the polycationic polymer to the absorbent gelling particles comprising a WAHP, and the absorbent material does not shift.
The bonds between the absorbent gelling particles to the glue microfibers, which in turn, are bonded to the carrier layer, prevent the absorbent gelling particles from shifting during the manufacturing process. The polycationic polymer bonded to the absorbent gelling particles prevents the particles from shifting after they swell with liquid. Consequently, the absorbent material of the invention has improved liquid acquisition speed and low rewetness when in use. It has been found that when the absorbent material is contacted with liquids, the absorbent material swells, imbibes such liquids into the absorbent gelling particles, and absorbs even under moderate confining pressures.
In a preferred embodiment of the present invention, the carrier layer is selected from the group consisting of a woven material and a nonwoven material.
These absorbent materials may further comprise the cellulose fibers dispersed in the absorbent gelling particles, wherein the cellulose fibers are adhered to the absorbent gelling particles by the glue microfibers.
Preferably, the absorbent material of present invention comprises from about 50% to about 90% of the absorbent gelling particle, from about 0.1% to about 10% of the polycationic polymer, from about 1% to about 10% of the thermoplastic polymeric microfiber and from about 5% to about 50% of the carrier layer by weight.
The invention further relates to a method of make the absorbent materials, and the absorbent articles comprising the absorbent materials.
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, attended claims and accompanying drawing.